When we raise our arm, the humeral head (top of the arm bone) comes closer to the acromion,

Front view right shoulder.

Back view right shoulder.

So imagine if the acromion is shaped differently, such as if it’s hooked downward where there isn’t as much space between it and the humeral head,

Lateral view right shoulder. Red and white is rotator cuff muscles and tendons.

Then a person with a hooked acromion is more likely to have issues with shoulder impingement and the rotator cuff (hello supraspinatus) than someone without.

That’s a fair explanation for why not everyone will handle overhead pressing the same.

-> That said, I very rarely have someone I can’t have overhead press. At worst, we might just have to be careful they don’t go all the way up, stopping a few degrees short. It’s rarely a big deal, once properly progressed into.

Going deeper with bench pressing

When people have shoulder pain benching it’s pretty much always at the bottom of the motion, when the bar is touching the chest,

Same goes for push-ups or DB benching. When the hands are closest to the chest is when pain is most likely.

Let’s go back to our anatomy. Notice this other structure at the front of the shoulder,

That’s the coracoid process. This can also have all kinds of shapes and sizes. It can hook down like the acromion. Notice the difference from left to right:

The morphometry of the coracoid process – its aetiologic role in subcoracoid impingement syndrome

It can be longer so it covers more of the humeral head:

Looking at the front of the right scapula.

It can be closer to the humeral head (lateral view of left shoulder now):

So let’s think about that with bench pressing. Think of the upper arm (humerus) like a lever. As the bottom (elbow) moves back, the top (humeral head) eventually starts moving forward,

If you’re someone with a coracoid process closer to the humeral head than someone else, then you’re humeral head is more likely to impinge the structures in-between the humeral head and coracoid process (such as the biceps tendon) than someone else.

When else does the elbow move back, thus eventually pushing the humeral head forward? The bottom of a bench press!

Let’s zoom in on this guy’s shoulder,

Getting some of our anatomy situated,

Now imagine two different coracoid processes. On the left it is flat and further away from the humeral head compared to on the right, where it’s hooked and closer,

It’s clear then on the right, as the elbow goes lower and the humeral head becomes more likely to move forward, it is more likely to impinge the coracoid.

I want to close out and say I haven’t seen a study specifically assessing this. There is research showing different shapes of the acromion and coracoid can cause an increased risk of rotator cuff tears, but I can’t say I’ve seen research showing coracoid process shapes change the risk of shoulder pain while benching. (Nor am I expecting a good study on this any time soon, though if someone is looking for a PhD thesis…) A study like this may not be feasible either. One of the studies I used above stated coracoid differences could not be precisely detected through imaging. They were only able to tease out these differences in cadavers. That said, I feel solid with the theory. A lot of bone anatomy operates this way.

Hat Tip to Menachem Brodie for bringing a research paper about this to my attention.

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So what do you do then if you still want to work your chest? If you still want to get a good upper body workout but keep your shoulders healthy?

And Yes, Agree, I too with there was research that could be done on this, AND to look at HOW each individual bench presses and overhead presses based on their personal structural variances.

I believe Ben Pakulski did a 6-8 min video on the difference striations and insertion angles of the pecs a few years back, which you’d probably appreciate as well. I think in particular the video is talking about Flies?